1. Field of the Invention
The disclosure relates to a method and apparatus for efficiently depositing patterns of films on a substrate. More specifically, the disclosure relates to a method and apparatus for depositing films on a substrate which may form part of an LED or other types of display.
2. Description of the Related Art
The manufacture of organic light emitting devices (OLEDs) requires depositing one or more organic films on a substrate and coupling the top and bottom of the film stack to electrodes. The film thickness is a prime consideration. The total layer stack thickness is about 100 nm and each layer is optimally deposited uniformly with an accuracy of better than +/−1 nm. Film purity is also important. Conventional apparatuses form the film stack using one of two methods: (1) thermal evaporation of organic material in a relative vacuum environment and subsequent condensation of the organic vapor on the substrate; or, (2) dissolution of organic material into a solvent, coating the substrate with the resulting solution, and subsequent removal of the solvent.
Another consideration in depositing the organic thin films of an OLED is placing the films precisely at the desired location. There are two conventional technologies for performing this task, depending on the method of film deposition. For thermal evaporation, shadow masking is used to form OLED films of a desired configuration. Shadow masking techniques require placing a well-defined mask over a region of the substrate followed by depositing the film over the entire substrate area. Once deposition is complete, the shadow mask is removed. The regions exposed through the mask define the pattern of material deposited on the substrate. This process is inefficient, as the entire substrate must be coated, even though only the regions exposed through the shadow mask require a film. Furthermore, the shadow mask becomes increasingly coated with each use, and must eventually be discarded or cleaned. Finally, the use of shadow masks over large areas is made difficult by the need to use very thin masks (to achieve small feature sizes) that make said masks structurally unstable. However, the vapor deposition technique yields OLED films with high uniformity and purity and excellent thickness control.
For solvent deposition, ink jet printing can be used to deposit patterns of OLED films. Ink jet printing requires dissolving organic material into a solvent that yields a printable ink. Furthermore, ink jet printing is conventionally limited to the use of single layer OLED film stacks, which typically have lower performance as compared to multilayer stacks. The single-layer limitation arises because printing typically causes destructive dissolution of any underlying organic layers. Finally, unless the substrate is first prepared to define the regions into which the ink is to be deposited, a step that increases the cost and complexity of the process, ink jet printing is limited to circular deposited areas with poor thickness uniformity as compared to vapor deposited films. The material quality is also typically lower, due to structural changes in the material that occur during the drying process and due to material impurities present in the ink. However, the ink jet printing technique is capable of providing patterns of OLED films over very large areas with good material efficiency.
No conventional technique combines the large area patterning capabilities of ink jet printing with the high uniformity, purity, and thickness control achieved with vapor deposition for organic thin films. Because ink jet processed single layer OLED devices continue to have inadequate quality for widespread commercialization, and thermal evaporation remains impractical for scaling to large areas, it is a major technological challenge for the OLED industry to develop a technique that can offer both high film quality and cost-effective large area scalability.
Finally, manufacturing OLED displays may also require the patterned deposition of thin films of metals, inorganic semiconductors, and/or inorganic insulators. Conventionally, vapor deposition and/or sputtering have been used to deposit these layers. Patterning is accomplished using prior substrate preparation (e.g., patterned coating with an insulator), shadow masking as described above, and when a fresh substrate or protective layers are employed, conventional photolithography. Each of these approaches is inefficient as compared to the direct deposition of the desired pattern, either because it wastes material or requires additional processing steps. Thus, there is a need for these materials as well for a method and apparatus for depositing high-quality, cost effective, large area scalable films.